Q: I loaned £15000 to a family member in 2017 of which £12,000 is still with them and the £3,000 they had returned to me this year but this money was immediately spent on some family expenditure.
A: Yes you have to pay Zakat on the money owed to you which you still hope to receive. You can either pay Zakat now until they repay you or, you can wait to get possession first and then backdate the Zakat payments for previous years.
As for the £3000 which you have already spent, if this amount was with you on your Zakat anniversary date then Zakat would have been due on it. On the other hand if you had spent this amount before your Zakat anniversary date then you do not need to pay Zakat on it. But you will still have to backdate the Zakat for previous years on this amount.
And Allah knows best!
Mufti Billal Omarjee